It is well known to use a shift register in a digital control device for a serial data transfer from a controller or processor to said control device especially if a small number of control lines or a small number of pins or signals for an integrated circuit shall be used. The serial data transfer is slow in comparison to a parallel one because a data word representing a control value has to be transmitted by subsequent rising edges of a clock signal shifting 1-bit data into a shift register. The complete control or data word has to be transmitted and received for an update of the output value of the control system. In cases of long data words represented by a large number of 1-bit data, the complete writing of the data word into a shift register takes a significant amount of time. On the other hand the direct digital synthesis technology provides very fast and precise control devices as e.g. a numerically controlled oscillator AD9850 manufactured by Analog Devices, which has a shift register lengths of 40 bits and allows an output frequency resolution of 0.0291 Hz with a 125 MHz reference clock applied. The output frequency can be digitally changed at a rate of up to 23 million new frequencies per second. The AD9850 comprises a 40-bit register, which can be loaded in a parallel or serial mode. In serial load mode, subsequent rising edges of a clock signal shift the 1-bit data on one pin through the 40 bits of programming information. After 40 bits are shifted through, a frequency update pulse is required to update the output frequency or phase provided by the control device. That means, where large shift registers are used, the complete writing will take a significant amount of time to update an output value of the control system.